Silylated perfluorinated ion-exchange microcomposite catalysts

ABSTRACT

This invention concerns a silylated porous microcomposite comprising a perfluorinated ion-exchange polymer entrapped within and highly dispersed throughout a network of inorganic oxide wherein the network and optionally the polymer have been modified with a silylating agent. These silylated microcomposites can be used in heterogeneous catalyst compositions for various chemical processes, such as in esterifications and acylations.

This application claim benefit to provisional application No. 60/042,768filing date Mar. 26, 1997.

FIELD OF THE INVENTION

This invention concerns catalysts comprising chemically modifiedperfluorinated ion-exchange microcomposites, processes for theirpreparation and their use as catalysts in chemical processes.

TECHNICAL BACKGROUND

K. A. Mauritz et al., Polym. Mater. Sci. Eng. 58, 1079-1082 (1988), inan article titled “Nafion-based Microcomposites: Silicon Oxide-filledMembranes”, discuss the formation of micro composite membranes by thegrowth of silicon oxide microclusters or continuous silicon oxideinterpenetrating networks in pre-swollen “NAFION®” sulfonic acid films.NAFION® is a registered trademark of E. I. du Pont de Nemours andCompany.

U.S. Pat. No. 4,038,213 discloses the preparation of catalystscomprising perfluorinated ion-exchange polymers containing pendantsulfonic acid groups on a variety of supports.

The catalyst utility of perfluorinated ion-exchange polymers containingpendant sulfonic acid groups, supported and unsupported has been broadlyreviewed: G. A. Olah et al., Synthesis, 513-531 (1986) and F. J. Wahler,Catal. Rev.-Sci. Eng., 1-12 (1986).

WO 95/19222 describes a porous microcomposite comprising aperfluorinated ion-exchange microcomposite containing pendant sulfonicacid and/or carboxylic acid groups entrapped within and highly dispersedthroughout a network of metal oxide. These catalysts are differentiatedfrom NAFION® supported catalysts in that by virtue of the preparation ofthe microcomposite catalyst, the polymer becomes intimately mixed with ametal oxide precursor in solution, and thus becomes thoroughly entrappedand highly dispersed throughout a resulting network of metal oxide. Withthe polymer being mechanically entrapped within the metal oxide networkand not merely on the surface of a support, as is the case in supportedcatalysts, the catalytic activity of these microcomposite catalysts issignificantly increased.

P. J. Stang, M. Hanack and L. R. Subramian, “PerfluoroalkanesulfonicEsters: Methods of Preparation and Applications in Organic Chemistry”,Synthesis, 1982, 85-126, discuss the utility of perfluoroalkanesulfonicesters, for example, trimethylsilyl trifluoromethanesulfonate (TMSOTf),as homogeneous catalysts for a range of reactions. P. A. Procopiou, S.P. D. Baugh, S. S. Flack and G. G. A. Inglis, J. Chem. Soc., Chem.Comm., 1996, 2625 disclose the utility of TMSOTf as an effectivehomogeneous catalyst for the acylation of alcohols with acid anhydrides.

Although a variety of reactions can be beneficially catalyzed by thecompounds and the composites cited above, there is still a need forheterogeneous catalysts of increased activity and selectivity andbroader applications.

SUMMARY OF THE INVENTION

The present invention provides a silylated porous microcomposite,comprising: a perfluorinated ion-exchange polymer containing pendantgroups selected from the group consisting of: sulfonic acid groups,silyl sulfonate groups, and a combination of said groups, wherein thepolymer is entrapped within and highly dispersed throughout a network ofinorganic oxide, said network having a plurality of silylated speciesbonded thereto.

The present invention also provides a process for the preparation of asilylated porous microcomposite, comprising the steps of: contacting aporous microcomposite comprising a perfluorinated ion-exchange polymercontaining pendant sulfonic acid groups or pendant metal sulfonategroups, wherein said polymer is entrapped within and highly dispersedthroughout a network of inorganic oxide, with a silylating agent undersilylating conditions for a time sufficient to convert a plurality ofhydroxyl groups of the inorganic oxide network to a silylated speciesand a portion of the sulfonic acid groups or metal sulfonate groups tosilyl sulfonate groups.

The present invention also provides an improved method for the acylationof an alcohol with an acid anhydride, the improvement comprising usingan effective amount of a catalyst composition comprising a silylatedporous microcomposite comprising a perfluorinated ion-exchange polymercontaining pendant groups selected from the group consisting of:sulfonic acid groups, silyl sulfonate groups, and a combination of saidgroups, wherein the polymer is entrapped within and highly dispersedthroughout a network of inorganic oxide, said network having a pluralityof silylated species bonded thereto.

DETAILED DESCRIPTION OF THE INVENTION

It is believed that key features of the present invention include themodification of a plurality of the residual hydroxyl groups of theinorganic oxide network to silylated species and optional modificationof all or a portion of the pendant sulfonic acid groups of aperfluorinated ion-exchange polymer of a porous microcomposite to silylsulfonate groups.

The present invention concerns the silylation of a porousmicrocomposite. By “porous microcomposite” is meant a compositioncomprising a perfluorinated ion-exchange polymer (PFIEP) containingpendant sulfonic acid groups, wherein said polymer is entrapped withinand highly dispersed throughout a network of inorganic oxide. The PFIEPmay optionally further comprise pendant carboxylic acid groups. Thepercentage of the perfluorinated ion-exchange polymer in themicrocomposite is from 0.1 to about 90% by weight and the size of thepores in the microcomposite is about 1 nm to about 75 nm, and themicrocomposite optionally further comprises pores having a size in therange of about 75 nm to about 1000 nm. Such microcomposites aredescribed in U.S. application Ser. No. 08/574,751, filed Dec. 19, 1995incorporated by reference herein and in the corresponding PCTpublication WO 95/19222. The microcomposite can be in any size or shapeto be utilized in the present invention, such as ground into particlesor shaped into spheres. The PFIEP is preferably, a sulfonated NAFION®PFIEP. The weight percentage of PFIEP preferably ranges from about 5% toabout 80%, most preferably from about 10% to about 15%. The inorganicoxide of the network is preferably silica, alumina, titania, germania,zirconia, alumino-silicate, zirconyl-silicate, chromic oxide, ironoxide, or mixture thereof; most preferably silica.

The inorganic oxide network of the present modified porousmicrocomposite has a plurality of silylated species bonded thereto. By“having a plurality of silylated species bonded thereto” is meant that aportion of the hydroxyl groups of the inorganic oxide network,preferably at least 50% of the hydroxyl groups, most preferably at least80% of the hydroxyl groups, are converted to a silylated species viareaction with a silylating agent, and this silylated species remainsbonded to the inorganic oxide network. As is known, after formation ofan inorganic oxide network, there are nunerous residual hydroxyl groups.This is because during network formation each of the inorganic atomsbecome constituents of a network structure via bonds to other inorganicatoms through oxygen but condensation to form these crosslinks does notgo to 100% completion; there are residual, uncrosslinked hydroxylgroups. For example, in the present case where the inorganic oxide ofthe network is silica, silanol (Si—OH) groups can be found as part ofthe network, and it is a plurality of the hydroxyl (—OH) groups of thesesilanols that are converted to silylated species which remain bonded tothe network.

By “silylated species” is meant a group having the formula—O)_(q)Si(R¹)_(4-q), wherein oxygen is bonded to the inorganic oxidenetwork, each R¹ is independently selected from the group consisting ofchloride, and a monovalent hydrocarbon radical, preferably C₁ to C₁₂alkyl or aryl, such as methyl, ethyl, propyl, butyl, and phenyl; mostpreferably methyl; and q is 1, 2 or 3. Thus, silylated species alsoinclude those instances where bridging and/or crosslinking has occurredduring silylation of the precursor hydroxyl groups.

The pendant groups of the PFIEP of the silylated porous microcompositecan be sulfonic acid groups, silyl sulfonate groups, or a combination ofthese two groups. The sulfonic acid groups are of the formula —SO₃H. Thesilyl sulfonate groups can be of the formula

—(SO₃)_(X)Si(R²)_(4-X)

wherein:

each R² is independently chloride, or a monovalent hydrocarbon radical,preferably C₁ to C₁₂ alkyl or aryl, such as methyl, ethyl, propyl,butyl, and phenyl, most preferably methyl; and x is 1, 2 or 3. Bridgingand/or crosslinking between two or more sulfonate groups is possible.For example, silyl sulfonate groups could be represented by thefollowing:

A representative example of a silyl sulfonate group is —SO₃Si(CH₃)₃.

The silylated microcomposites of the present invention differ from theirprecursor (i.e., the porous microcomposites) in their wettability. Thesilylated microcomposites are hydrophobic.

This invention further provides a process for the preparation of saidsilylated porous microcomposite comprising contacting a porousmicrocomposite, as defined above, or a porous microcomposite havingpendant metal, preferably silver, sulfonate groups, with an effectiveamount of a silylating agent under silylating conditions for a timesufficient to convert a plurality of hydroxyl groups of the inorganicoxide network to silylated species and a portion of the sulfonic acidgroups or metal sulfonate groups to silyl sulfonate groups.

By “silylating agent” is meant a substance capable of silylating theinorganic oxide network and, optionally all or a portion of the sulfonicacid groups of the PFIEP. The silylating agent can comprise a compoundrepresented by the formula Si(R³)_(4-n)X_(n), wherein X is chloride ortrifluoromethanesulfonate; each R³ is independently selected from amonovalent hydrocarbon radical, preferably a C₁ to C₁₂ alkyl or aryl,such as methyl, ethyl, propyl, butyl, and phenyl, most preferablymethyl; and n is an integer from 1 to 4.

Certain silylating agents have more than one leaving group (bindingsite) on the silicon atom, for example (C₆H₅)₂SiCl₂ and C₆H₅SiCl₃. Forthose cases where n is greater than 1, it is possible that an X remainson the silicon atom and becomes part of the silyl sulfonate group orsilylated species. For those cases, X is preferably chloride. Inaddition, it makes possible the bridging and/or crosslinking between twoor more silylated species and/or between two or more silyl sulfonategroups.

Alternatively, the silylating agent can comprise a compound representedby the formula R⁴R⁵R⁶SiNHSiR⁷R⁸R⁹, wherein R⁴, R⁵, R⁶, R⁷, R⁸, and eachindependently selected from the group consisting of chloride and amonovalent hydrocarbon radical, preferably a C₁ to C₁₂ alkyl or aryl,such as methyl, ethyl, propyl, butyl, and phenyl, most preferablymethyl. Preferred silylating agents include trimethylsilylchloride,trimethylsilyl trifluoromethanesulfonate and hexamethyldisilazine.

Contact with the silylating agent can be accomplished in a number ofways, for example, in a gas phase, in a liquid phase or via sublimation,depending on the silylating agent selected.

It is preferred that the reactant material, the porous microcomposite,as defined above, or the porous microcomposite having PFIEP with pendantmetal sulfonate groups, be substantially dry and that the presentprocess be carried out under essentially anhydrous conditions. Smallamounts of water can be overcome by using an excess of the silylatingagent.

A solvent, essentially non-reactive with the silylating agent, can beemployed, or the present process can be carried out using excesssilylating agent as the solvent/suspension media.

The silylation reaction of the present process can be carried out at anyconvenient temperature. The use of the reflux temperature of thesolvent/suspension media is particularly convenient.

During the present process, the pendant sulfonic acid groups and/or thependant silver sulfonate groups of the PFIEP can remain unchanged or allor a portion of said pendant groups can be converted to silylatedsulfonate groups. After completion of the reaction, excess silylatingreagent can be removed by heating the product in vacuum.

The silylated porous microcomposite product can be filtered and washedwith a solvent. Suitable solvents include, but are not limited toalkanes, such as hexane and heptane, and chlorinated solvents such asmethylene chloride.

The utility of the silylated porous microcomposites of the presentinvention is in catalyst compositions including use, for example, inesterification or acylation reactions.

The present invention further provides an improved method for theacylation of an alcohol with an acid anhydride, the improvementcomprising using an effective amount of a catalyst compositioncomprising a silylated porous microcomposite comprising a perfluorinatedion-exchange polymer containing pendant groups selected from the groupconsisting of: sulfonic acid groups, silylated sulfonate groups, and acombination of said groups, wherein the polymer is entrapped within andhighly dispersed throughout a network of inorganic oxide, said networkhaving a plurality of silylated species bonded thereto.

Preferably, the perfluorinated ion-exchange polymer contains sulfonicacid groups and trimethylsilyl sulfonate groups and is about 10 to about15% by weight of the microcomposite. It is also preferred the inorganicoxide of the network is silica and that the silylated species is a grouphaving the formula —OSiR¹R²R³, wherein: R¹, R², and R³ are eachindependently selected from the group consisting of: chloride, and amonovalent hydrocarbon radical.

EXAMPLES

A 13 wt % NAFION® resin in silica microcomposite catalyst, referred toin the examples below as the unmodified microcomposite, was prepared asdescribed in the next paragraph using a NAFION® PFIEP NR 005 solution.NAFION® PFIEP NR 005 solution is available from DuPont NAFION® Products,Fayetteville, N.C., is also known as NAFION® SE-5110, and is preparedfrom resin which is approximately 6.3 tetrafluoroethylene molecules forevery perfluoro(3,6-dioxa-4-methyl-7-octenesulfonyl fluoride) molecule(CF₂═CF—O—(CF₂CF(CF₃)—O—CF₂CF₂—SO₂F). After hydrolysis of the resin, thePFIEP has an equivalent weight of approximately 1070. NAFION® PFIEPsolutions can be purchased from Aldrich Chemical Co., Milwaukee, Wis.,or PFIEP solutions generally can be prepared using the procedure of U.S.Pat. No. 5,094,995 and U.S. Pat. No. 4,433,082.

204 g of tetramethoxysilane (TMOS), 33 g of distilled water and 3 g of0.04 M HCl was stirred for 45 min to give a clear solution. To 300 mL ofa NAFION® PFIEP solution was added 150 mL of a 0.4 M NaOH solution,while the PFIEP solution was being stirred. After addition of the NaOHsolution, the resulting solution was stirred for a further 15 min. TheTMOS solution was added rapidly to the stirred PFIEP solution. Afterabout 10-15 sec, the solution gelled to a solid mass. The gel was placedin an oven and dried at a temperature of about 95° C. over a period ofabout 2 days followed by drying under vacuum overnight. The hard,glass-like product was ground and passed through a 10-mesh screen. Thematerial was then stirred with 3.5M HCl for 1 hour (with 500 mL ofacid), followed by washing with 500 mL deionized water. The solid wascollected by filtration. Acidification, washing and filtration wererepeated a total of 5 times and after the final wash the solid was driedunder vacuum at 100° C. for 24 hours.

EXAMPLE 1 Preparation of a Silylated Microcomposite UsingTrimethylsilylchloride

10 g of an unmodified microcomposite (as prepared above) was dried at150° C. in vacuum overnight. Under nitrogen, this was added totrimethylsilylchloride (50 g) and the material was refluxed undernitrogen for 24 hours. The excess trimethylsilylchloride was removedunder vacuum to yield the silylated microcomposite. The silylatedmicrocomposite was very hydrophobic.

EXAMPLE 2 Preparation of a Silylated Microcomposite UsingHexamethyldisilazine

10 g of an unmodified microcomposite (as prepared above) was dried at150° C. in vacuum overnight. Under nitrogen, this was added tohexamethyldisilazine (50 g) and the material was refluxed under nitrogenfor 24 hours. The hexamethyldisilazine excess was removed under vacuumto yield the silylated microcomposite. The silylated microcomposite wasvery hydrophobic.

EXAMPLE 3 Preparation of a Silylated Microcomposite Using TrimethylsilylTrifluoromethanesulfonate

10 g of an unmodified microcomposite (as prepared above) is dried at150° C. in vacuum overnight. Under nitrogen, this is added totrimethylsilyl trifluoromethanesulfonate (50 g) and the material isrefluxed under nitrogen for 48 hours and triflic acid is evolved. Thetrimethylsilyl trifluoromethanesulfonate and triflic acid are removedunder vacuum to yield the silylated microcomposite.

What is claimed is:
 1. A silylated porous microcomposite, comprising: aperfluorinated ion-exchange polymer containing pendant groups selectedfrom the group consisting of silyl sulfonate groups and a combination ofsilyl sulfonate groups and sulfonic acid groups, wherein the polymer isentrapped within and highly dispersed throughout a network of inorganicoxide, said network having a plurality of silylated species bondedthereto.
 2. The microcomposite of claim 1 wherein the inorganic oxide ofthe network is silica.
 3. The microcomposite of claim 2, wherein thesilylated species is a group having the formula —O)_(q)Si(R¹)_(4-q),wherein: oxygen is bonded to the inorganic oxide network, each R¹ isindependently selected from the group consisting of: chloride, and amonovalent hydrocarbon radical; and q is 1, 2 or
 3. 4. Themicrocomposite of claim 1 wherein all or a portion of the pendant groupsare silyl sulfonate groups having the formula —(SO₃)_(x)Si(R²)_(4-x)wherein each R² is independently selected from the group consisting of:chloride and a monovalent hydrocarbon radical; and x is 1, 2 or
 3. 5.The microcomposite of claim 4 wherein all or a portion of the pendantgroups are trimethylsilyl sulfonate groups.
 6. The microcomposite ofclaim 1 wherein the perfluorinated ion-exchange polymer containssulfonic acid groups and trimethylsilyl sulfonate groups and saidpolymer is about 10 to about 15% by weight of the microcomposite.
 7. Aprocess for the preparation of a silylated porous microcomposite,comprising the steps of: contacting a porous microcomposite comprising aperfluorinated ion-exchange polymer containing pendant sulfonic acidgroups or pendant metal sulfonate groups, wherein said polymer isentrapped within and highly dispersed throughout a network of inorganicoxide, with a silylating agent under silylating conditions for a timesufficient to convert a plurality of hydroxyl groups of the inorganicoxide network to a silylated species and a portion of the pendantsulfonic acid groups or metal sulfonate groups to silyl sulfonategroups.
 8. The process of claim 7 wherein the silylating agent comprisesa compound having the formula —Si(R³)_(4-n)X_(n), wherein: each R³ isindependently selected from a monovalent hydrocarbon radical; X ischloride or trifluoromethane sulfonate; and n is an integer from 1 to 4.9. The process of claim 1 wherein the silylating agent is selected fromthe group consisting of: trimethylsilylchloride, trimethylsilyltrifluoromethane sulfonate, and hexamethyldisilazine.
 10. The process ofclaim 7 wherein the silylating agent comprises a compound having theformula R⁴R⁵R⁶SiNHSiR⁷R⁸R⁹, wherein R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ are eachindependently selected from the group consisting of: chloride and amonovalent hydrocarbon radial.
 11. The method of claim 10 wherein theinorganic oxide of the network is silica.
 12. The method of claim 11wherein the inorganic oxide of the network is silica and the silylatedspecies is a group having the formula —O)_(q)Si(R¹)_(4-q), wherein:oxygen is bonded to the inorganic oxide network, each R¹ isindependently selected from the group consisting of: chloride, and amonovalent hydrocarbon radical; and q is 1, 2 or 3.